[Andy Bentley]

I'm looking to take my first step in EV ownership and have a deposit reserved on a Nissan Leaf 24kWh 2016 model from a dealer. The vehicle has only 1600 miles; apparently it belonged to an elderly gentleman who found it too confusing and so he traded it in as soon as his lease contract was up. The dealer claims that low mileage means low risk and he produced a battery test report with five stars saying it was "excellent". I must admit it looks an immaculate vehicle and it drives beautifully so I put a deposit on it. However, I delayed a final decision until he (reluctantly) agreed to me plugging an OBD diagnostic reader and using Leaf Spy Lite to see the underlying battery info.

Today, I connected to the vehicle OBD port to find that the SoH is 90.1% and Hx=87.6%. I was pleased to see only one rapid charge and 81 L1/L2 charges. But that makes a charge every 19.5 miles, is it possible the battery has been overcharged?

I must admit I'm struggling to make sense of the Leaf Spy battery data. The 90% SoH is lower than I'd expected after only 1600 miles, but after looking at the excellent "24 kWhAge vs Health" graph collected from data on this forum, it does seem to be a reasonable figure for a 3.5 year old battery - assuming that time has a bigger impact on cell chemistry rather than the number of miles travelled.

My question relates to Leaf Spy's cell battery graph (see attached screen shot): cell #38 looks to be odd-one-out at 3.955V compared to the others (4.005V) with a maximum 61mv spread. Does this indicate a weak cell? The colour of this battery is different, which I understand is Leaf Spy's indication that the BMS is slowly discharging it - is this correct? Am I right in saying that this is just a snapshot in time and the cells should equalise after a a few gentle discharge/recharge cycles?

Before I commit to purchase, I would really appreciate advice/comment from Leaf owners who understand this battery data more than me!

Many thanks in advance
Andy

 

[DBMandrake]

I'm looking to take my first step in EV ownership and have a deposit reserved on a Nissan Leaf 24kWh 2016 model from a dealer. The vehicle has only 1600 miles; apparently it belonged to an elderly gentleman who found it too confusing and so he traded it in as soon as his lease contract was up. The dealer claims that low mileage means low risk and he produced a battery test report with five stars saying it was "excellent". I must admit it looks an immaculate vehicle and it drives beautifully so I put a deposit on it. However, I delayed a final decision until he (reluctantly) agreed to me plugging an OBD diagnostic reader and using Leaf Spy Lite to see the underlying battery info.

Today, I connected to the vehicle OBD port to find that the SoH is 90.1% and Hx=87.6%. I was pleased to see only one rapid charge and 81 L1/L2 charges. But that makes a charge every 19.5 miles, is it possible the battery has been overcharged?

You can't overcharge the battery in an EV, once it's fully charged it will stop charging. It sounds like the car was only ever driven short distances (approx 20 miles) before being charged again, which would be consistent with very low mileage.

I must admit I'm struggling to make sense of the Leaf Spy battery data. The 90% SoH is lower than I'd expected after only 1600 miles, but after looking at the excellent "24 kWhAge vs Health" graph collected from data on this forum, it does seem to be a reasonable figure for a 3.5 year old battery - assuming that time has a bigger impact on cell chemistry rather than the number of miles travelled.

Calendar age is probably a bigger factor than mileage, especially if the car has sat at a high state of charge a lot of the time, which is likely the case here if the car was frequently recharged by a small amount and did a very low overall mileage.

My question relates to Leaf Spy's cell battery graph (see attached screen shot): cell #38 looks to be odd-one-out at 3.955V compared to the others (4.005V) with a maximum 61mv spread. Does this indicate a weak cell? The colour of this battery is different, which I understand is Leaf Spy's indication that the BMS is slowly discharging it - is this correct? Am I right in saying that this is just a snapshot in time and the cells should equalise after a a few gentle discharge/recharge cycles?

It depends what the reason for the imbalance is, and unfortunately there's no way to tell by this one snapshot in time. If it's a faulty cell, the balancing system won't be able to do anything about it. If the cell's SOC has just got out of balance with other cells (but why ?) then eventually it would balance itself with enough charge cycles.

The BMS will actually be trying to discharge all cells except the lowest one during charging. From what I've read, the balancing system on the Leaf is very weak with only a 10mA (anyone know for sure ?) discharge rate available. If that's true, that's only 1/10th of the 100mA discharge rate of the balancing system on my Ion.

I did a cell swap on my Ion a few months ago and due to a silly mistake I didn't adequately balance the SoC of the replacement cells, as a result they were about 50mV lower than the other cells at a full state of charge. It took nearly 2 months of normal daily driving (35 miles a day commute and one charge per day, so about 40 charge cycles and 1400 miles driving) for the BMS to finally get all the cells into perfect balance.

With larger capacity cells and a weaker balancing system I would say that a 60mV imbalance at full charge would take a lot longer to be corrected in a Leaf, certainly a lot more than "a few" charging cycles.

So it could be months of daily driving and charging before the balance would be corrected - but by then you would have no come back if it turned out it was indeed a faulty cell and the balance did not come right.

One other possbility is that the car has had a cell swap under warranty (but again, why) and whoever swapped the cell didn't get it in balance properly before fitting and essentially made the same mistake I did. There is precidence too as there is a thread on here of someone who had cells swaped in their Leaf by a dealer and the cell balance was miles out (far worse than 50mV) and ended up going back twice to the dealer to try to get it sorted. (Maybe someone can find that thread)

I'm not a Leaf owner (yet...) but I do have some cell swapping and testing experience and I would be a little bit cautious due to the imbalance shown on a car with such low mileage, you really have no way of knowing without a few months of driving and charging whether that cell is faulty or whether it's just out of balance for some reason.

 

[Johnny Read]

Are you willing to say the price you negotiated for the car?

 

[srichards]

I'd probably avoid any car with such low mileage. Is there any service record to prove it's been used lightly but regularly rather than been stuck in storage for ages as it was a duffer?

It's more of a risk than a regularly used one. There's no way of knowing if it was left sat at 100% plugged in most of the time either.

 

[Layzee]

If the price is good it may be worth a punt, its possible that with a few deep discharge and charge cycles that the cell might balance, if it doesnt let the battery discharge until the cell voltage reach about 3.7v and see iv it triggers a weak cell warning if it does screen shot it and go back to the dealer and ask them to do a cvli test if it shows up as a weak cell then they should replace it under warranty.
I had exactly the same problem Nissan did a warranty replacement on mine made a big difference to the range !

Oh and forget the dealer battery repot it is useless with a capital U

 

[Hermit Dave]

Biggest factor in battery degradation is ageing. 3% per year drop in SoH is a common occurrence with Leaf Li-ion cells.

You still have sufficient warranty left to ask them for a battery test (post purchase). A single LeafSpy screenshot isn't likely to tell the whole story.

You need to observe cell voltage at various stages of charge followed by test while car is in use.

- Leaf 30 kWh
Sent from mobile phone so please mind the typos

 

[Hermit Dave]

Biggest factor in battery degradation is ageing. 3% per year drop in SoH is a common occurrence with Leaf Li-ion cells.

You still have sufficient warranty left to ask them for a battery test (post purchase @Layzee method). A single LeafSpy screenshot isn't likely to tell the whole story.

You need to observe cell voltage at various stages of charge followed by test while car is in use.

- Leaf 30 kWh
Sent from mobile phone so please mind the typos

 

[Andy Bentley]

You can't overcharge the battery in an EV, once it's fully charged it will stop charging. It sounds like the car was only ever driven short distances (approx 20 miles) before being charged again, which would be consistent with very low mileage.

Calendar age is probably a bigger factor than mileage, especially if the car has sat at a high state of charge a lot of the time, which is likely the case here if the car was frequently recharged by a small amount and did a very low overall mileage.

It depends what the reason for the imbalance is, and unfortunately there's no way to tell by this one snapshot in time. If it's a faulty cell, the balancing system won't be able to do anything about it. If the cell's SOC has just got out of balance with other cells (but why ?) then eventually it would balance itself with enough charge cycles.

The BMS will actually be trying to discharge all cells except the lowest one during charging. From what I've read, the balancing system on the Leaf is very weak with only a 10mA (anyone know for sure ?) discharge rate available. If that's true, that's only 1/10th of the 100mA discharge rate of the balancing system on my Ion.

I did a cell swap on my Ion a few months ago and due to a silly mistake I didn't adequately balance the SoC of the replacement cells, as a result they were about 50mV lower than the other cells at a full state of charge. It took nearly 2 months of normal daily driving (35 miles a day commute and one charge per day, so about 40 charge cycles and 1400 miles driving) for the BMS to finally get all the cells into perfect balance.

With larger capacity cells and a weaker balancing system I would say that a 60mV imbalance at full charge would take a lot longer to be corrected in a Leaf, certainly a lot more than "a few" charging cycles.

So it could be months of daily driving and charging before the balance would be corrected - but by then you would have no come back if it turned out it was indeed a faulty cell and the balance did not come right.

One other possbility is that the car has had a cell swap under warranty (but again, why) and whoever swapped the cell didn't get it in balance properly before fitting and essentially made the same mistake I did. There is precidence too as there is a thread on here of someone who had cells swaped in their Leaf by a dealer and the cell balance was miles out (far worse than 50mV) and ended up going back twice to the dealer to try to get it sorted. (Maybe someone can find that thread)

I'm not a Leaf owner (yet...) but I do have some cell swapping and testing experience and I would be a little bit cautious due to the imbalance shown on a car with such low mileage, you really have no way of knowing without a few months of driving and charging whether that cell is faulty or whether it's just out of balance for some reason.

Thanks for your advice. I've decided against buying this vehicle and will look for another.

It's been a valuable learning experience using Leaf Spy to see underneath the dealer's sanitised battery reports and I'll insist on using before buying - and walk out if they refuse!

I was initially confused by Leaf Spy's auto-scaling vertical axis for cell voltage and I was surprised how little the difference should normally be.

I think you're right about the Leaf's weak balancing, I found a post saying that the bleed resistors are 430ohms, which would give around 10mA.

It'll take a bit of time to get my head around Li-ion cell behaviour. In the past I've had design experience of small lead acid, NiCd and NiMH battery chargers, but scaling up to 400V DC is quite daunting! Kudos to you for doing your own cell swapping.

 

[Andy Bentley]

If the price is good it may be worth a punt, its possible that with a few deep discharge and charge cycles that the cell might balance, if it doesnt let the battery discharge until the cell voltage reach about 3.7v and see iv it triggers a weak cell warning if it does screen shot it and go back to the dealer and ask them to do a cvli test if it shows up as a weak cell then they should replace it under warranty.
I had exactly the same problem Nissan did a warranty replacement on mine made a big difference to the range !

Oh and forget the dealer battery repot it is useless with a capital U

Thanks for the advice - I hope your vehicle is now maintaining its charge. Your experience with Nissan is not a good advert for their competence with these batteries.

The dealer was asking £10950 and wouldn't reduce because of the condition and very low mileage. I don't think the salesmen fully appreciated my concern that low mileage isn't necessarily the same advantage for EVs as it is for ICE vehicles.

The leaf spy screen shot certainly exposed the uselessness of their battery report. It was the first time I've used it .. and I'll insist on using it in all viewings from now on!

As my wife will be using this car for relatively low mileage, then I thought the risk of buying the car and seeing if we can rebalance cells could take a long time with no guarantee of success. Just my luck that the weak cell would hold out until just after the battery warranty expires in 18 months time before triggering the error threshold.

The dealer has some 2017 models, with more realistic mileage, for a few hundred pounds more - I'll check these out.

 

[Andy Bentley]

I'd probably avoid any car with such low mileage. Is there any service record to prove it's been used lightly but regularly rather than been stuck in storage for ages as it was a duffer?

It's more of a risk than a regularly used one. There's no way of knowing if it was left sat at 100% plugged in most of the time either.

Advice duly noted thanks. I think I'll give this one a miss.

The service and MOT records showed steady mileage progression, but assuming a regular average of 9 miles a week then it could have been left at 100% charge for quite some time overall.

 

[Andy Bentley]

Biggest factor in battery degradation is ageing. 3% per year drop in SoH is a common occurrence with Leaf Li-ion cells.

You still have sufficient warranty left to ask them for a battery test (post purchase @Layzee method). A single LeafSpy screenshot isn't likely to tell the whole story.

You need to observe cell voltage at various stages of charge followed by test while car is in use.

- Leaf 30 kWh
Sent from mobile phone so please mind the typos

Thanks for the feedback. I've learned a lot from following the suggested thread.

On balance (pun intended) I think I'll give this vehicle a miss. Seems a bit of a risk: I'll take a look at slightly newer but higher mileage alternatives at the dealer.

 

[JaC]

Hi Andy, Take a look at my 2017Leaf30 in the classifieds. It's got brilliant SOH (98%) and is a gem.
Oh, it's in Norwich, but I may be persuaded to deliver

 

[Andy Bentley]

Hi Andy, Take a look at my 2017Leaf30 in the classifieds. It's got brilliant SOH (98%) and is a gem.
Oh, it's in Norwich, but I may be persuaded to deliver

Hi, I didn't know there was a classifieds section on this forum: thanks for the heads-up! I see your car is no longer for sale; I'm not surprised it looks immaculate.

With no experience of on-the-go EV charging and erring on safe side of range anxiety, I'd tended to kept my search radius fairly local, within 50 miles of Banbury. I guess as confidence grows I'll try longer distances, but unlike jumping in a petrol-fueled vehicle, EV journeys appear to require meticulous route planning, allowance for contingencies and drinking lots of coffee at each charge stop!

 

[JaC]

Hi Andy, I had a change of plans due to a recent bereavement so it's going to stay for a while.
I got mine from Grimsby (120miles) and took a run out to look at a couple there before buying.
I Leafspied them first before committing to buy. Mine was 92+% SOH when I got it, and 96% after I had the BMS update done.
As it had only ever had 2 rapid charges, it soon benefited from regular rapids and rose to 98% where it has stayed for several months.
Yes planning your route is important, but not too onerous once you get the hang of it. I plan long trips with 100% charge at the start and
aim for a charger 80 miles away (arriving with 20%), this gives me contingency in case it's U/S. I top up to 90% and set off for another
60 - 70 miles away, etc. I try to pick a charger with a back up not too far away just in case. I use Zapmap and it's been invaluable.
I initially had to register with all the local suppliers and those en route to family (seven I think) which was a pain,
but from this year all new chargers will use contactless.
Good luck with your search.
[BTW The 2017 Tekna30 that I also Leafspied looks to be still available, it was similar to mine 92+% SOH at the time, with low rapids
eBay: 324022051706 ]